It is well known in the art involving fluids used in the drilling, completion and workover of wells in earth formations, to include either a fresh water solution, or a non-saturated brine solution, or a saturated brine solution, polymers, starches and bridging solids, for example, as discussed in the SPE Paper No. 35332, entitled "Design and Application of Brine-based Drilling Fluids", authored by R. Swarthout and R. Pearcy, presented at the International Petroleum Conference and Exhibition in Mexico, in Villahermosa, Mexico, Mar. 5-7, 1996. The completion of workover fluids using similar formulations are also discussed in U.S. Pat. Nos. 4,822,500; 4,175,042; 4,186,803 and 4,369,843.
U.S. Pat. No.4,822,500 makes use of starch which is considered to be an epichlorohydrin crosslinked, hydroxypropyl starch manufactured from a low amylopectin maize starting material. This patent also discloses the combination of xanthan gum with the low amylopectin starch, as well as particle solids such as sized salt, for example, sized sodium chloride, in formulating well treating fluids.
Moreover, British Patent No. 2,086,923 assigned to Baroid Technology, Inc., the assignee of this present application, discloses the combination of various polysaccharide gums, such as xanthan gum, with various starch derivatives. On page 3 of the British Patent No. 2,086,923, for example, there is teaching that exemplary starch derivatives are the carboxyalkyl starch ethers such as carboxymethyl starch and carboxyethyl starch; hydroxyalkyl starch esters, such as hydroxethyl starch and hydroxypropyl starch; and mixed starch ethers such as: carboxylalkyl hydroxyalkyl starch, e.g., methyl hydroxyethyl starch; alkyl carboxyalkyl starch, e.g., ethyl carboxymethyl starch. Exemplary polysaccharide gums include: the bipolymers such as xanthomonas (xanthan) gum; galactomannan gums, such as guar gum, locust bean gum, tara gum; glucomannan gums; and derivatives thereof, particularly the hydroxyalkyl derivates. For other exemplary polysaccharide gums see U.S. Pat. Nos. 4,021,355 and 4,105,461. Especially preferred hydrophilic polymers are xanthan gum (XC polymer), carboxymethyl cellulose and hydroxyethel starch.
Various other starches can also be used in formulating drilling, completion and workover fluids, as is well known in this art, for example, as discussed in Composition and Properties of Oil Well Drilling Fluids, Fourth Edition, published by Gulf Publishing Co., Houston, Tex., 1980, authored by George R. Gray, H. C. H. Darley and Walter F. Rogers, at its pages 548-552. The use of xanthan gum in such fluids is also discussed in the same reference, pages 554-556.